Manufacture of dibenzanthrone compounds



. is formed (Houben,

Patented Mar. 5, 1935 7 MANUFACTURE 0F DIBENZANTHRONE COMPOUNDS EdwardT.- HowelL Milwaukee, Wis., assignor to E. I.,.'du;Pont de Nemours &Company, ,Wil-- v mington, DeL, a corporation of Delaware No Drawing.

-23 Claims.

This invention relates .to the manufacture of vat dyestuffs of theanthraquinone series. More particularly, this invention dealswith animproved process for the manufacture of diben- 7 zanthrone compounds bythe alkaline fusion of benzanthrone or its derivatives.

, The caustic fusion of benzanthrone to dibenzanthrone has receivedconsiderable study. in the art. The earliest processes as suggested byBally (U. S. Patent 818,992) involved the heating of benzanthrone inmelted causticpo-tash at a" temperature of'180to 230 C; or the fusion ofa benzanthrone derivative, for instance, chloro-benzanthrone, in a meltof equal parts of caustic potash and absolute alcohol at' atemperature'of about 150 to 180 C. (U. S. Patent 818,336). I1Later'various modifications were, applied to these originalprocesses, most ofthem involving'the addition of various diluents or assistants to thefusion'bath. Among these, it has been claimed that "the addition ofreducing agents such as dextrinefdextros'e, f

fructose andvarious aldehydes produce beneficial results. (U.'S.,Patents1;4'78,027; 1,844,381; 1,845,246 and 1,849,826) Nevertheless, the aboveprocessesleave much to be improved as regards quality of the product.Althou'gh'the crude dyestuff obtained-in many cases correspondspractically to the theoretical yield ex pected from the initial quantityof: benzanthrone, the product is invariably contaminated withisodibenzanthrcne, and its tinctorial value is low. In manycases thecrude" product contains 'as high as 40% of inert, vat insoluble-material,-and the portion that is vattable is'fre- 'quently' sorich in"isodibenz'anthrone as to seriously affect the shade of thedyeing, andrender the dyestuff unfit for the purpose intended.-

Most of these processes are in substance twostage, processes. At first2,2'-dib enzanthronyl Das Anthracen und die Anthrachinone,, pages 774775). The formation of this intermediate is particularly favored Wherethe benzanthrone and caustic alkali are mixed in the cold and heated upjointly to the optimum fusion temperature. (The latter is generallyaround 180 to 230- C.) At the higher temperature, the intermediate ringcloses "to produce dibenzanthrone in leuco form, which uponv aerationgives the dyestufL. It appears, however, that not all of 'theintermediate 2,2- dibenzanthronyl is .50 ring closed. Under theinfluence of the higher temperature, partof the intermediate --is disrupted and recombinedlin a Application December 27, 1932, v Serial No.648,979 r diiferent'manner to give isodibenzanthrone and otherundesirable by-products.

I have now found that if benzanthrone is fused with alcoholic potash inthe presence {of an oxidizing agent, and preferably in the-presence ofan inhibitor such as potassium acetate, an exceptionally high yield ofdibenzanthrone in a state of high purity may beobtained; The productobtained is generally quantitative in yield and substantially free ofeither yet insoluble impurities or isodibenzanthrone. The tinctori'alyield of the product i s ';40"to 60% greatenthan that obtained by directcaustic fusion of benzanthrone, which is undoubtedly I due bothtotheincreas'ed yield ofdibenzanthrone and. to its higher purity'whichcauses .its-dyeings to be of'true shade and' improved brightness. Sincean oxidizing agent is the direct opposite of a reducing agent, the aboveresult is truly astonishing in view of the prac- 'tice in the art asabove referred-to.

As oxidizing agent, practically any known agent adapted to work inalkaline medium may be employed. The field is practically unlimited, asboth inorganic and organic oxidizing agents may be resorted towith'great success. .Thus, 'the following'oxidizing agents have been.found by me to give improved results: metallic-peroxides; alkali metalchromates, bichromates, and permanganates; .metal nitrates or chlorates;cupric' oxides or salts; ferric compounds; nitrobenzene sulfonic acids.

-With most oxidizing agents, best results are obtained if the'agent isadded after-the beginning of the reactionand preferably at that stagewhen formation of 2,2'-dibenzanthronyl apparently proceeds at a highrate." In other words, the "oxidizing agent'shouldbeadded after thetemperature of the mass has reached about 100-150 C.,'and hasbeenimaintain'ed at this temperature for some time. The rule,'however,is not absolute and varies considerably with the particular oxidizingagent selected. Thus in thecase of basic ferric'acetate, I have addedthe entire oxidizing agent at the beginning, andbefore the mass washeatedup to the-optimum temperature. The fusion product,ho'wevenexhibited fully 40 to greater tinctorial yield thandibenzanthrone'obtained'by direct'fusion; 1

Inert diluents may be added if desired, for instance, kerosene,naphthalena diphenyl, and the like.

The theory of the reaction is not quite under- I stood. As stated above,it'appears that 2,2'edi- "benzanthronyL more correctly, its'leuco-Io1-m,-is 1 improvement may vary within wide limits.

first formed in the reaction. The presence of the oxidizing agentapparently assists its conversion into leuco-dibenzanthrone, withoutgiving it the opportunity to decompose, under the influence of the hightemperature, into intermediate products which would otherwise leadeventually to iso-dibenzanthrone or to alkali-insoluble byproducts. Thelatter effect is particularly brought out by the use of an inhibitorsuch as potassium acetate. This agent seems to regulate and slow downthe rate of reaction whereby to prevent the formation of the undesirableby-products prior to the final heating up stage, where the oxidizingagent begins to exert its effect. Any other means of controlling therate of reaction during the first stage of the process Without, however,cooling the mass to a point where fusion will not proceed at all, wouldappear to give equally good results. For instance, sodium acetate,potassium propionate, or other alkali metal salts of lower aliphaticacids may be used to accomplish the same purpose. The quantity ofoxidizing agent required'for The theoretical quantity appearsto be theequivalent of atom of oxygen per mole of benzanthrone. However,allowance must be made for the fact that the oxygen equivalent of agiven oxidizing agent in alkaline alcoholic medium is not the same asthat in aqueous acid. medium. Generally it is less, therefore a greaterquantity of the oxidizing agent is necessary. Thus, in the case ofpotassium chlorate I found that 1 to 2 moles per mole of benzanthronegives best results. In the case of potassium permanganate, as low asmoles per mole'of benzanthrone was sufficient. In the case of cupricoxide 4 moles were found necessary. Moderate excesses of oxidizing agentproduce no ill effects upon the product.

I have also found it advantageous to use a lower alcohol-potash ratiothan used heretofore in similar fusions in the art. Generally speaking,the ratio of alcohol to caustic potash should not exceed 1:2 by weight.

Without limiting my invention to any particular procedure, the followingexamples are given to illustrate my preferred mode of operation.

Parts given are by weight.

Example 1 25 parts of fused potassium acetate are added to 25 parts ofmethanol and stirred until substantially dissolved. 150. parts ofcaustic potash are added, and the mass is heated to 125-130" C. 250parts of molten naphthalene are now introduced, and then 50 parts ofpurified benzanthrone, M. P. 168-170 C., are added. The temperature isthen raised at a uniform rate to 140 C. during half an hour. There arethen added 50 parts of finely ground natural manganese dioxide(approximately 86% MnOz) during 5-10 minutes. Heating is continueduniformly to a gentle reflux (about 215) and held furic acid with ared-violet color, and gives dyeings upon cotton of the shadecharacteristic of pure dibenzanthrone.

If in the above example, 25 parts of fused sodium acetate or 25 parts offused potassium propionate are used instead of 25 parts fused potassiumacetate, very similar results are obtained.

Example 2 250 parts of molten naphthalene, previously heated to 130l35C. are added to a melt of 25 parts of methanol, 25 parts offusedpotassium acetate and 150 parts .of caustic potash flakes all previouslyheated to 125 C. 50- parts of benzanthrone are then added at the sametemperature. The temperature is then raised at a uniform rate duringabout hour to 135 C., when 25 parts finely ground potassium permanganateare added. Heating is'continued so that the temperature rises uniformlyto a gentle refluxing of the naphthalene and the fusion mass is stirredat'this temperature (210-215 C.) for hour and worked up as in Example 1.Dibenzanthrone is thus obtained in a very high tinctorial yield.

7 Example 3 260 parts of high boiling kerosene are heated to 130 C. andadded to a melt of 25 parts of methanol, 25 parts of fused potassiumacetate and '150 parts of caustic potash flakes, heated to 130 C. Thetemperature of the mixture is ad- J'usted to 125 C., and '50 parts, ofbenzanthrone are added. The whole mass is heated during about hour to135 C., 50 parts manganese dioxide (86%) are then added during about5-10 minutes and the temperature of the mass is raised to 220 C. during/2-% hour. The fusion mass is maintained at a temperature of 215-220 C.for another hour; cooled to 150- 160 C., and the kerosene layer isdecanted off. The fusion mass is then transferred into ,cold water,steam distilled free of traces of kerosene, filtered and washed. Theproduct, when freed of manganese compounds as in Example 1, consists ofdibenzanthrone exceptionally free from impurities.

Example 4 The fusion is carried out as in Example 2, with the exceptionthat 62.5 parts potassium chromate are used instead of 25 partspotassium permanganate, and the chromium hydroxide is removed after thefusion by a simple acid extraction. The product so obtained ispractically of identical quality with that of the previous examples.

H Example .5

50 parts of benzanthrone are added at 125 C. to a melt of 25 parts ofmethanol, 25 parts of fused potassium acetate, 150 parts of causticpotash flakes, and 250 parts of naphthalene, mixed hot in the ordergiven. The temperature is then raised during about hour to 135 C. and 79parts of finely powdered cupric oxide are added. Heating is continued sothat the refluxing point (210-215 C.) is reached during about hour.After being maintained at this ternperaturefor hour more, the fusionmass is allowed to cool with stirring to 8590 C. and diluted with 600parts warm water. After steam distillation of the naphthalene, copper isremoved by known methods and the dyestuif filtered off and dried.Dibenzanthrone is thus ob- Cal tained'oiv a. quality practicallyidentical with that of the products previously described. i

Example 6' A melt of parts of methanol, 25 parts of fused potassiumacetate and 150-parts of caustic potash flakes is heated to 130 C. andthen diluted with 250 parts of'molten naphthalene. parts of benzanthroneare then added at 125 C. and the temperature raised to 135 C. duringabout hour; 75 parts of finely powdered pow tassiurn dichromate are thenadded, the'tell peratureis raised slowly to the refluxingpoint of themixture, and maintained at that point with stirring for hour. The melt,which becomes very thick toward the end, is freed from naphthalene, bydecantation, transferred to cold wa-.

, ter, and steam distilled-free of traces of diluent.

After filtering and washing, chromium compounds are einoved byextraction with dilute sulfuric acid. The product so obtained consistsof dibenzanthrone havingsubstantially the same properties as abovenoted.

Example 7 A melt of 37.5 parts of methanoh 12.5 parts of fused potassiumacetate and 156 parts of causti potash flakes is heated to135- C. anddiluted with 250 parts molten naphthalene. 59 .parts of 'benzanthroneare then added at 125 0., and the'temperature is raised during abouthour to 135 C.

raised to the refluxing point (ZN-215 C.). Aiter stirring hour at thistemperature, the fusion mass is cooledto 125-13G C. and vacuum isgradually applied to the fusion kettle. The naphthalene distils overwithout foaming at 120-l25 C. under 28 inches' vacuum and is re Example8 Amelt is prepared as in Example 7, using 15 parts of methanol, 15parts of fused potassium acetate, 90 parts of caustic potash, and 150parts of naphthalene. benzanthrone (obtained according nto U. S. PatentNo.;1,614,398) are then added at-l25'C.,, and the temperature is raisedto 135 Cduring hour.- After adding 15 parts of finely powdered potassiumchlorate, heating is continued until a temperature of 190 C. is reached.The fusion mass isthen stirred hourfat. 198-200 C. and worked uppbycoolingto about 125. 0., drowning in 900 parts of cold water, followedby aeration, steam distillation of the naphthalene, filtration andWashing. The productv so obtained consists of dimethoxyv dibenzanthronehayingless than 3% vat-insoluble impurities. 7

Example 9 30 parts of benzanthrone and 30 parts of pow dered potassiumchlorate are added at 185440 C.

50 parts of finely powdered potassium, chlorate are then added and thetemperature is the recovery of chi 15 parts of BZZ-mBthOXYe the spiritofthis invention.

to a melt of 30 parts ofniethanol, 7.5 parts fused potassium acetate and99' parts icaustic potash. The fusion mass is heatedgradually to 210C.',

.allowing-alcoholto distil off, and is held at 21G- 215" C.untildyes'tufi formation is complete, which usually requires 5; to 1hour. The melt may then he drowned in Water, or cooledand diluted withwater, aerated; filtered; washed, and dried. Di-

henzanthrone of high purity and high tinctorial yield is so obtained.Emmple 10 I henzanthrcne are added at 125 C.

5*) parts of 195% ethyl alcohol, 25

- 50 parts 0 to a melt 0 parts of caustic pota." and ZQO'parts ofnaphthalene, mixed hot in order given. After raising the temperature to135gC. during /g-fiA. hours, 62.5 parts of finely! powderedjpotassiuandichroinate e added; and the temperature is then raised to andmaintained with continued stirring eltto85" (3., is dilutedwith' partsof warm water and worked; up ,by steam distillation of thenaphthalenennd extraction of chromium us of dilute sulfuric acid; .The

compounds by dyestuif so bnzanthro. as described above.

ed consists or .high grade di- Exampl ejll 1? par of. molten naphthaleneare added to eltcr 01.5 parts of methanol, 12.5 parts of urn acetate'and159 parts of caustic potash heated to ISO-135. There are then added 50parts-of finely powdered-basic ferric acetate and 25" parts ofpurifiedhenz'anthrone. The temperature is raised to the refluxing pointof the rriixtma-iAfter stirring 012% hour at this tern pr-nature (215C)the melt is allowed to cool to ahout lfiif C. and diluted with 600"parts of W- water. The product is worked up by steam distillation toremote naphthalene, filtered, and tl i eiilter-eake is hoiled'in anexcess of hydrochloric acid to remove iron compounds. It is filtered.Washed and dried. The product so obtained "consists of dibenzanthron'eof substantially the same high qualities above descdhed.

Example 12;

A melt oi 37.5 partsof-methanolj'mfi parts of fused potassium acetateand 150 parts of causticpotash flakes is heate'dto 135 C. and dilutedwith 250 parts n1olten naphthalene.-The temperature is then adjusted to125 C. and 737.5 parts fused potassium acetate, 15%) parts of actioallythe properties,

of finely ground hasicferric acetate and 25 parts ofalpha-'-chlor-b'enzanthrone; obtained, for example, from alphachloranthraquinone and glycerine, are added. The temperature is thenraised to about 215 C. and the reaction mixture stirred underrefiux' forhour. After cooling to 90- 196 product is isolatedv by filtering andWashing,

followedjby extraction withhydrochloric acid to I'Cll'iOVd'iIOl'lhydroxides. "The dyestufi so' obtained gives a somewhat greener shade ofblue than 'dihenaanthrone itself and is of excellent yield and greatpurity; I

It will be understood'that many variations and modifications arepossiblein the preferred procedures above indicated Without departing from Thus,instead of any of the oxidizing agents indicatedahove, many otheroxidizing agents may (3., S60 parts warm water are added, and thenaphthalene is removed by distillation.

be used. In one test, following the procedure of Example 1, I havereplaced the 50 parts of manganese dioxide by parts of finely groundm-nitrobenzene-sodium sulfonate (68%) with highly satisfactory results.Mixtures of oxidizing agents are sometimes advantageous.

The proportion of alcohol may be varied somewhat, depending on the kindof alcohol and the kind of oxidizing agent, but the amount used shouldnot be less than those indicated in the examples at risk of formation ofmore or less isodibenzanthrone. Generally, a ratio of /6 to part ofalcohol to each part of caustic potash will give satisfactory results,with an optimum at about 1:4.

It has been found that prolonged heating such as 3 to 4 hours, asspecified in some of the older types of fusions, is not necessary, butthat dyestuif formation is usually complete in to 1 hour after themaximum temperature of the fusion has been reached. The latter may varybetween 180 and 230 C.

Instead of working up the fusion by steam distillation, a solvent fornaphthalene, such as toluene, may be added to the partially cooled melt,followed by filtration and washing the filter cake with a light solventto remove the heavier diluent. Alternatively, vacuum distillation may beresorted to, as illustrated in Example 7. After steam distillation ofthe diluent, the dyestuff may be separated from insoluble inorganicmatter by vatting, filtering and aeratingthe filtrate.

Many other variations and modifications are possible without departingfrom the spirit of this.

invention. a v

' I am aware of U. S. Patent No. 1,564,423, wherein benzanthrone isfirst converted to 2,2'-dibenzanthronyl and the latter is isolated andconverted into dibenzanthrone or an oxidation derivative thereof eitherby further caustic fusion in the absence of an oxidizing agent or byoxidizing in acid medium. My novel process differs from the above inseveral important respects, of which the following two are of majorsignificance. In my improved process no intermediate isolation steps arenecessary, and the oxidation is effected in alkaline medium. That2,2'-dibenzanthronyl could be ring closed by oxidation in alkalinemedium has apparently not been known to date. On the contrary, asalready pointed out above, it was believed in the art that the causticfusion is favored by the presence of reducing media. I may add further,that the final dyestuffs obtainable by my process are of superior purityand tinctorial yield as compared with the dyestuffs when the procedureof said U. S. Patent No. 1,564,423 is followed.

I claim:

1. The process of producing a dibenzanthrone which comprises fusing abenzanthrone with alcoholic potash in the presence of an oxidizingagent.

2. The process of producing a dibenzanthrone which comprises fusing abenzanthrone with alcoholic potash in the presence of an oxidizingagent, the alcohol potash ratio being less than 1 to 2 by weight.

3. The process of producing a dibenzanthrone which comprises fusing a'benzanthrone with alcoholic potash in the presence of an oxidizingagent, the alcohol potash ratiov being less than 1 to 2 by weight, and.the amount of oxidizing agent being not less than the alkalineequivalent of A atom of oxygen per mole of benzanthrone;

4. The process of producing a dibenzanthrone which comprises fusing 'abenzanthrone with alcoholic potash in the presence of an oxidizing agentand an alkali-metal salt of a lower aliphatic acid.

5. A process as in claim 4, the alcohol: potash ratio being less than1:2 by Weight, and the amount of oxidizing agent being not less than thealkaline equivalent of atom of oxygen per mole of benzanthrone.

6. A process for producing dibenzanthrone which comprises heating a meltof benzanthrone in alcoholic potash to a temperature between and 150 C.,adding an oxidizing agent and. further heating the mass at a temperaturefavoring the formation of dibenzanthrone.

'7. A process as in claim 6, the quantity of a1- cohol being less thanby weight of the quantity of caustic potash.

8. A process as in claim 6, the fusion mass containing further an inertdiluent.

9. A process as in claim 6, the fusion mass containing furthernaphthalene as a diluent.

10. A process as in claim 6, the fusion mass containing further analkali metal salt of a lower fatty acid.

11. A process as in claim 6, the fusion mass containing furtherpotassium acetate.

12. A process for producing dibenzanthrone which comprises heating amelt of benzanthrone in alcoholic potash to a temperature between 180and 150 C., adding an oxidizing agent and further heating the mass at atemperature of between 180 and 230 C.

13. A process for producing dibenzanthrone which comprises preparing amelt comprising benzanthrone, alcohol, caustic potash, an oxidizingagent and an alkali metal salt of a lower aliphatic acid at atemperature not less than 100 C. and not above 150 C., and heating saidmelt further to a temperature between 180 and 230 C. until dyestuifformation is substantially complete.

14. Aprocess as in claim 13, the quantity of alcohol being less than byweight of the quantity of caustic potash.

15. A process as in claim 13, the melt containing further an inertdiluent.

16. The process of producing dibenzanthrone which comprises fusingbenzanthrone in a melt of caustic alkali, an alcohol, an inert diluentand and alkali-metal salt of a lower aliphatic acid at a temperature ofabout to C., adding an oxidizing agent, raising the temperature tobetween and 230 C. and continuing the heating until dyestufi formationis substantially comple e.

17. The process of producing dibenzanthrone which comprises fusingbenzanthrone in a melt of caustic potash, methanol, naphthalene andpotassium acetate at a temperature of about 120 to 150 C., adding anoxidizing agent, raising the temperature to between 180 and 280 C. andcontinuing the heating until dyestuff formation is substantiallycomplete.

18. 'A process as in claim 17, the alcohol being present in a ratio notless than M; and not more than by weight of the caustic potash.

19. A process for producing dibenzanthrone which comprises fusingbenzanthrone in the presence of caustic potash under conditions favoringthe formation of 2,2-dibenzanthronyl, adding an oxidizing agent andfurther fusing the mass at a temperature favoring the formation ofdibenzanthrone.

20. A process of producing dibenzanthrone 10 in alkaline medium.

22. The process of producing dibenzanthrone which comprises oxidizing2,2-dibenzanthrony1 in its own highly alkaline mass of formation.

23. In the process for producing diloenzanthrone which comprises fusingbenzanthrone in the presence of caustic potash under conditions favoringthe formation of 2,2-dibenzanthronyl and then adjusting the conditionsto effect ringclosure to dibenzanthrone, the step which comprisescarrying out at least the latter part'of the fusion in the presence ofan oxidizing agent.

EDWARD T. HOWELL.

